Comparative proteomic analysis of Salmonella typhimurium LT2 and its hisG gene inactivated mutant

Identification of novel inhibitors against Escherichia coli utilizing HisC as a target from histidine biosynthesis pathway

Escherichia coli is a gram-negative bacterial pathogen that poses a significant challenge both clinically and epidemiologically. Large numbers of multi-drug resistant E. coli have emerged in the last decade, because of the selection pressure generated by the inadequate use of antibiotics. Although research to combat antibiotic resistance has been going on extensively but still lags in the rate of development of newer antibiotics. Therefore, newer approaches are required to speed up the rate of discovery of antibiotics. Computational methods for screening of inhibitors have made a significant contribution to the discovery of novel antimicrobials. The present study utilized histidinol-phospho aminotransferase (HisC) as a target. HisC is an enzyme that plays a crucial role in the biosynthesis of histidine and its absence in mammals makes it an attractive drug target. A ZINC library of 5000 natural compounds was screened against HisC (PDB ID: 1FG7) using PyRx and the first 500 hits were selected for secondary screening after sorting the result on the basis of binding score. Fifteen compounds passed the secondary filter ADME and out of these five passed toxicity filters; the best among five hits was selected on the basis of its binding score and inhibition constants. Further, molecular dynamics simulations and free binding were computed of selected five compounds and two natural compounds ZINC402598829 and ZINC31157928 complexed with HisC were found as highly stable. Overall, our results indicated that these natural sources could be used as potential HisC inhibitors.Communicated by Ramaswamy H. Sarma.

In Vitro and In Vivo Studies of Heraclenol as a Novel Bacterial Histidine Biosynthesis Inhibitor against Invasive and Biofilm-Forming Uropathogenic Escherichia coli

Globally, urinary tract infections (UTIs) are one of the most frequent bacterial infections. Uropathogenic Escherichia coli (UPEC) are the predominant etiological agents causing community and healthcare-associated UTIs. Biofilm formation is an important pathogenetic mechanism of UPEC responsible for chronic and recurrent infections. The development of high levels of antimicrobial resistance (AMR) among UPEC has complicated therapeutic management. Newer antimicrobial agents are needed to tackle the increasing trend of AMR and inhibit biofilms. Heraclenol is a natural furocoumarin compound that inhibits histidine biosynthesis selectively. In this study, for the first time, we have demonstrated the antimicrobial and antibiofilm activity of heraclenol against UPEC. The drug reduced the bacterial load in the murine catheter UTI model by ≥4 logs. The drug effectively reduced bacterial loads in kidney, bladder, and urine samples. On histopathological examination, heraclenol treatment showed a reversal of inflammatory changes in the bladder and kidney tissues. It reduced the biofilm formation by 70%. The MIC value of heraclenol was observed to be high (1024 µg/mL), though the drug at MIC concentration did not have significant cytotoxicity on the Vero cell line. Further molecular docking revealed that heraclenol binds to the active site of the HisC, thereby preventing its activation by native substrate, which might be responsible for its antibacterial and antibiofilm activity. Since the high MIC of heraclenol is not achievable clinically in human tissues, further chemical modifications will be required to lower the drug's MIC value and increase its potency. Alternatively, its synergistic action with other antimicrobials may also be studied.

Repurposing of FDA approved drugs against uropathogenic Escherichia coli: In silico, in vitro, and in vivo analysis

Urinary tract infections (UTIs) are a serious health concern worldwide. Treatment of UTIs is becoming a challenge as uropathogenic Escherichia coli (UPEC), which is the most common etiological agent, has developed resistance to the main classes of antibiotics. Small molecules that interfere with metabolic processes rather than growth are attractive alternatives to conventional antibiotics. Repurposing of already known drugs for treating infectious diseases could be an attractive avenue for finding novel therapeutics against infections caused by UPEC. Virtual screenings enable the rapid and economical identification of target ligands from large libraries of compounds, reducing the cost and time of traditional drug discovery. Moreover, the drugs that have been approved by the FDA have low cytotoxicity and good pharmacological characteristics. In this work, we targeted the HisC enzyme of the histidine biosynthetic pathway as enzymes of this pathway are absent in humans. We screened the library of FDA-approved drugs against HisC via molecular docking, and four hits (Docetaxel, Suramin, Digitoxin, and Nystatin) showing the highest binding energy were selected. These were further tested for antibacterial activity, which was observed only for Docetaxel (MIC value of 640 μg/ml); therefore, Docetaxel was further tested for its efficacy in vivo in murine catheter UTI model and antibiofilm activity using crystal violet staining and scanning electron microscopy. Docetaxel inhibited biofilm formation and reduced the bacterial load in urine, kidney, and bladder. Docking studies revealed that Docetaxel acts by blocking the binding site of HisC to the native substrate by competitive inhibition. Docetaxel may be a potential new inhibitor for UPEC with antibacterial and antibiofilm capability.